How Do You Verify an Agent Fix When It Only Fails One Run in Twenty?

Such-Process5697 · reddit · 2026-09-09

A developer describes a thorny agent engineering problem: a multi-step customer-record cleanup agent occasionally deletes rows it should update, failing roughly once in twenty runs, discovered only via row-count drift. Deterministic replay tests only the orchestration, real runs take 4 minutes against a production database, and a trimmed fixture reproduces 1 in 3 but may introduce new bugs. The post captures a fundamental agent-eval dilemma: the failure rate is exactly what you need to measure — and what's most expensive to measure.

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